本文从理论上推导了谱分析中最大后延M的取值,并且从理论和实际计算中得出了样本长度和其隐含周期之间的关系。只要抽样是平稳的,样本长度并非一定要求太长,仅略为超过其隐含周期的长度即可。但谱分析绝非是万能的。如果样本中仅含有两个波动,且当这两个波动的周期相差一个整数倍或更大时,这两个波动才可以通过谱分析分辨出,反之就会歪曲了其隐含周期。由此可见,在具体应用时,应作一些滤波和去掉趋势是必要的。因而这将对广大气象、地理科学工作者以及其它相邻学科的科研工作者具有重要的参考价值。

The present paper include three aspects of question. (1) how to determine the value of Maximum Lab M in theory? (2) what is the re:itionship hecween the length of sample series N and the period T which is contained in this sample series? (3) how much is reliability of the period T which is disclosed by spectra analysis? The value of Maxmum Lag M is expected to be high if spectra unbiased estimation is con-sidered. At the same time, however, this value is expected limited under the consideration of re-duction variance of spectra estimation. It is advisable then that the value of Maximum Lag M be selected as 1/3 to 1/10 of the length of sample series N in both theory and practical calcula-tions.